Update changelog

Author: danielnelson

CHANGELOG.md

@@ -49,6 +49,7 @@
 - [#3136](https://github.com/influxdata/telegraf/issues/3136): Fix webhooks input address in use during reload.
 - [#3258](https://github.com/influxdata/telegraf/issues/3258): Unlock Statsd when stopping to prevent deadlock.
 - [#3319](https://github.com/influxdata/telegraf/issues/3319): Fix cloudwatch output requires unneeded permissions.
+- [#3351](https://github.com/influxdata/telegraf/issues/3351): Fix prometheus passthrough for existing value types.
 
 ## v1.4.3 [unreleased]